In recent years, a metal microparicle has been wanted in wide fields such as a catalyst, a conductive material, a magnetic material, a secondary electron releasing material, a luminescent material, a heat absorber, an energy storage material, an electrode material, and a coloring material; and a metal microparticle having suitable particle diameter for its purpose has been considered to be necessary. Both a precious metal and a non-precious metal have been receiving an attention; and for example, nickel, a typical non-precious metal, is being widely used as a magnetic material for a magnetic recording medium and the like, a catalyst, a laminated ceramic condenser, an inner conductive material of a substrate, an electrode material, and so forth. Especially in view of a thermal shrinkage property of a metal, a metal microparticle having narrow particle diameter distribution is wanted; and in accordance with its performance and ease in handling, metal micorparticles having different particle diameters need to be produced selectively. In view of the above, in order to industrially utilize a metal microparticle, not only a method for producing it stably with a large scale but also a method with which a metal microparticle having a particle diameter thereof controlled can be produced highly precisely and efficiently is eagerly wanted.
There are many methods for producing a metal microparticle; in a gas phase method, a method such as spray pyrolysis of a solution that contains a metal ion, shown in the Patent Document 1, is generally used. However, in this method, it is difficult to produce particles having uniform particle diameter and crystal type; and in addition, there are problems of a large manufacturing equipment, a high energy cost, and so forth. In a liquid phase method, a method such as a so-called polyol reduction is generally known as shown in the Patent Document 2; in this method, however, specific means to control particle diameter of the particles to be produced has not been reported. Especially in a batch process thereof, it is difficult to obtain uniform particle diameter thereby causing problems such as generation of the problematic coarse particles and classification thereof; and therefore, control of the particle diameter of metal particles has been very difficult.
Applicant of the present invention provided a method for producing a metal microparticle such as the one reported in the Patent Document 3; however, a specific method for controlling the particle diameter of metal microparticles to be produced has not been disclosed in the Patent document 3.